Early wireless communication systems were used only for voice communication, while more recent wireless communication systems also allows for non-voice data communication and combinations of both types, for example video calls and downloading of movies. A circuit switched core network handles, in most cases, end to end voice call setup and mobility management in the wireless communication system, while a packet switched core network handles end to end packet call setup and mobility management in the wireless communication system.
The present day wireless communication systems face a great challenge from the increasing usage of sophisticated wireless devices, such as smart phones. These wireless devices are able to handle multiple active connections (Radio Access Bearers, RABs) simultaneously and thereby support both data and voice traffic: updating various applications, sending and receiving e-mails in the background while making or receiving voice call. This mixture of circuit and packet switched connection types requires some consideration. For example, voice communication is generally more delay sensitive than non-voice data communication, and should be handled accordingly, e.g. by prioritizing circuit switched call setup before packet switched setup, otherwise the users will experience bad availability. Signaling of core network domain indicators was introduced in 3GPP Rel-6, wherein a wireless device includes a domain indicator indicating if a connection establishment is desired to a circuit switched core network or to a packet switched core network. A network node is thereby able to prioritize the connection establishment based on the domain indicator.
However, in various scenarios and for different reasons, packet switched connections are nevertheless set up prior to circuit switched connections. As a particular example of a scenario when this problem may occur, the circuit switched fallback (CSFB) mechanism can be mentioned. CSFB provides voice services for Long Term Evolution (LTE) subscribers by reusing the Global System for Mobile Communications/Universal Mobile Telecommunications System (GSM/UMTS) network. When a wireless device in the LTE network initiates or receives a voice call, a mobility management entity (MME) requests an Evolved Node B (eNB) to redirect the wireless device to the UMTS network or to the GSM network, and connections within the LTE network are released. For example, if the wireless device has an active LTE data session when a voice call is initiated or received, the wireless device will remember the status of the data connection at a Non Access Stratum (NAS) layer and it will initiate signaling connection setup towards both the packet switched domain and the circuit switched domain when the wireless device is successfully redirected from LTE to UMTS network. In this scenario it often happens that the packet switched core network is able to establish a radio access bearer for the wireless device faster than the circuit switched core network establishes its radio access bearer.